The invention relates to manholes, and particularly to that area adjacent the top of the manhole. By spanning the upper portion thereof, it eliminates or reduces surface water infiltration between the manhole casting and the adjacent adjusting rings or components, commonly referred to as the "chimney", which form the upper portion of the manhole and their interface with the manhole casting.
A manhole casting may sit directly on a manhole cone or there may be adjusting rings between the cone and the casting. Existing manhole chimneys have also had the casting shimmed with wood or bricks, with mortar placed in the gaps in between. Manhole chimneys of the past have been constructed with precast adjusting rings or of brick or block and are used on manholes constructed with precast sections, brick or block, or cast in place concrete.
Most inventive activity relating to the subject matter of the invention has been directed to sealing pipe sections and sealing pipes to manholes at the bottom of a manhole to prevent water infiltration at lower levels of the manhole. However, after the pipes have been sealed to the bottom of the manhole, and the manhole constructed and backfilled to approximately the level of the top of the casting, surface water infiltration between the casting and manhole chimney has been possible. This is a problem leading to increased sewage treatment costs, uncomfortable working conditions, and other problems inherent when unanticipated fluids leaked into existing manhole structures.
Two prior patents have been issued which relate to improvements to the placing of manhole castings. U.S. Pat. No. 3,308,727 provides a cushion for a manhole cover but does not seal it. U.S. Pat. No. 4,029,425 provides an extension for a manhole. With the latter invention a seal of the extension can be provided in the form of a bicycle tire innertube which can be inflated after the extension is in place which should prevent infiltration at the level of the bicycle innertube.